neuron. Hormones may also function as neuro-
transmitters.
The appropriate balance of neurotransmitters is
essential for neurologic function, as some neuro-
transmitters are excitory (allow nerve impulses to
move from one neuron to another) and others are
inhibitory (block nerve impulses). Neurotransmit-
ters have specific functions. The BLOOD–BRAIN BAR-
RIER allows the NERVOUS SYSTEM to maintain
different levels of neurotransmitters in the BRAIN
and in the body. Acetylcholine, for example, is
essential in the brain for functions of cognition
and memory. A diminished level of acetylcholine
in the brain is among the hallmark characteristics
of ALZHEIMER’S DISEASE. DOPAMINE is critical for
movement; PARKINSON’S DISEASEdevelops when the
cells in the brain that produce dopamine die.
Dopamine also facilitates nerve impulses that acti-
vate the brain’s pleasure centers. Monoamine oxi-
dase (MAO), serotonin, and NOREPINEPHRINE are
key to mood. ANTIDEPRESSANT MEDICATIONSact by
altering the balance of these three chemicals in
the brain. In the body, acetylcholine conducts
electrical impulses between neurons and MUSCLE
cells to facilitate movement. EPINEPHRINEand nor-
epinephrine conduct electrical impulses in the
HEART.
For further discussion of neurotransmitters
within the context of the structures and functions
of the nervous system, please see the overview
section, “The Nervous System.”
See also AGING, NEUROLOGIC CHANGES THAT OCCUR
WITH; HORMONE.
organic brain syndrome A collective term for
disorders of cognition (thought and logic) and
memory that arise from physical changes that take
place in the BRAIN. Numerous neurologic and
metabolic disorders can cause organic brain syn-
drome, as can head trauma and INFECTION, such as
ENCEPHALITIS. Organic brain syndrome sometimes
becomes an ambiguous diagnosis when there are
few distinct or apparent causes to explain mental
deterioration in people who are elderly. However,
the physical changes that occur in the brain to
produce organic brain syndrome are more com-
mon in old age though are not inevitable aspects
of aging.
COMMON DISORDERS ASSOCIATED
WITH ORGANIC BRAIN SYNDROME
ALZHEIMER’S DISEASE DEMENTIA
ENCEPHALITIS HEART ATTACK
hepatic NEUROPATHY HUNTINGTON’S DISEASE
HYDROCEPHALY HYPOXIA
long-term ALCOHOLISM MENINGITIS
PARKINSON’S DISEASE SEPTICEMIA
STROKE substance abuse
TRANSIENT ISCHEMIC ATTACK(TIA) TRAUMATIC BRAIN INJURY(TBI)Symptoms and Diagnostic Path
The presentation and severity of symptoms varies
with the underlying condition and other health
factors. Symptoms extend over time and often
worsen with time. Key symptoms include- confusion, disorientation, and DELIRIUM
- difficulty carrying out tasks that require
thought, logic, and reasoning such as shopping
or traveling to and from home - diminished ability to interact with others in
social settings - diminished ability to independently carry out
activities of daily living such as bathing, dress-
ing, and preparing meals - lapses of memory, especially inability to
remember recent events
The diagnostic path begins with a ROUTINE MED-
ICAL EXAMINATIONto assess health overall and a
NEUROLOGIC EXAMINATIONto evaluate brain function
and cognitive abilities. Because symptoms can
result from electrolyte imbalance, HORMONEdistur-
bances, high or low BLOOD GLUCOSE(sugar) levels,
and other factors, the routine medical examina-
tion typically includes a complete blood count
(CBC) and other blood tests. The doctor may also
conduct a basic cardiovascular evaluation, includ-
ing ELECTROCARDIOGRAM(ECG) and measurement of
BLOOD PRESSURE. A number of health conditions
that can cause cognitive disturbances become
more common with advanced age, some of which
are easily treatable such as HYPOTHYROIDISM, HYPER-
TENSION, ADRENAL INSUFFICIENCY, and cardiac
ARRHYTHMIA. The doctor may also conduct diagnos-
tic imaging procedures such as COMPUTED TOMOGRA-272 The Nervous System